This invention relates to the formation of elution gradients for gradient elution chromatography.
It is known in gradient elution chromatography to pump two or more different fluids to a mixer and to use a magnetic stirrer to mix the two fluids. The start and composition of the gradient is controlled by a programmer.
In the prior art gradient systems of this class, the gradient program is initiated in response to a timer or by manual initiation or by a fixed program for repetitive runs. The mixer operates independently of the program control.
The prior art apparatus and methods for establishing the gradient have several disadvantages, such as: (1) the pumps for the fluids may be at different pressures at the time of the start of the chromatographic run and, in such a case, the gradient is distorted at the start because the uneven pressure causes the fluid from the lower pressure source to be held back or even for the fluid from the higher pressure source to flow into the lower pressure source; and (2) under some circumstances, it is difficult to obtain suitable mixing unless a reservoir is used that is too large for certain shaped gradients. These disadvantages are more significant in microliquid chromatography and supercritical chromatography. The pumps used for these two types of chromatography are usually single-stroke syringe pumps whose relatively large fluid volume aggregates the first disadvantage, above.